Simplify the following expression: $k = \dfrac{4rs}{5rs} - \dfrac{rs + 2s}{5rs}$ You can assume $r,s,t \neq 0$.
Solution: Since the expressions have the same denominator we simply combine the numerators: $k = \dfrac{4rs - (rs + 2s)}{5rs}$ $k = \dfrac{3rs - 2s}{5rs}$ The numerator and denominator have a common factor of $s$, so we can simplify $k = \dfrac{3r - 2}{5r}$